Up to now the cyanide-containing waste has been collected in destruction facilities within the plant, usually large basins, where destruction has taken place by oxidation with sodium hypochlorite. Small plants have to collect their wastes in closed vessels which have to be transferred to destruction plants with concomittant high costs. It is also known to destroy the cyanide contents of solutions by anodic oxidation, but the technology developed up to now has been complicated and requires long electrolyzing periods. Examples of the latter type of techniques are found in U.S. Pat. No. 3,764,499, Swiss patent specification No. 444,066 and published Swedish patent application No. 77-12278-6.